Electrocatalytic Hydrogenation Using Palladium Membrane Reactors.

Hydrogenation is a crucial chemical process employed in a myriad of industries, often facilitated by metals such as Pd, Pt, and Ni as catalysts. Traditional thermocatalytic hydrogenation usually necessitates high temperature and elevated pressure, making the process energy intensive. Electrocatalytic hydrogenation offers an alternative but suffers from issues such as competing H2 evolution, electrolyte separation, and limited solvent selection. This Perspective introduces the evolution and advantages of the electrocatalytic Pd membrane reactor (ePMR) as a solution to these challenges. ePMR utilizes a Pd membrane to physically separate the electrochemical chamber from the hydrogenation chamber, permitting the use of water as the hydrogen source and eliminating the need for H2 gas. This setup allows for greater control over reaction conditions, such as solvent and electrolyte selection, while mitigating issues such as low Faradaic efficiency and complex product separation. Several representative hydrogenation reactions (e.g., hydrogenation of C=C, C≡C, C=O, C≡N, and O=O bonds) achieved via ePMR over the past 30 years were concisely discussed to highlight the unique advantages of ePMR. Promising research directions along with the advancement of ePMR for more challenging hydrogenation reactions are also proposed. Finally, we provide a prospect for future development of this distinctive hydrogenation strategy using hydrogen-permeable membrane electrodes.

The Promising Seesaw Relationship Between Activity and Stability of Ru-Based Electrocatalysts for Acid Oxygen Evolution and Proton Exchange Membrane Water Electrolysis.

The development of electrocatalysts that are not reliant on iridium for efficient acid-oxygen evolution is a critical step towards the proton exchange membrane water electrolysis (PEMWE) and green hydrogen industry. Ruthenium-based electrocatalysts have garnered widespread attention due to their remarkable catalytic activity and lower commercial price. However, the challenge lies in balancing the seesaw relationship between activity and stability of these electrocatalysts during the acid-oxygen evolution reaction (OER). This review delves into the progress made in Ru-based electrocatalysts with regards to acid OER and PEMWE applications. It highlights the significance of customizing the acidic OER mechanism of Ru-based electrocatalysts through the coordination of adsorption evolution mechanism (AEM) and lattice oxygen oxidation mechanism (LOM) to attain the ideal activity and stability relationship. The promising tradeoffs between the activity and stability of different Ru-based electrocatalysts, including Ru metals and alloys, Ru single-atomic materials, Ru oxides, and derived complexes, and Ru-based heterojunctions, as well as their applicability to PEMWE systems, are discussed in detail. Furthermore, this paper offers insights on in situ control of Ru active sites, dynamic catalytic mechanism, and commercial application of PEMWE. Based on three-way relationship between cost, activity, and stability, the perspectives and development are provided.

Quantifying cell viability through organelle ratiometric probing.

Detecting cell viability is crucial in research involving the precancerous discovery of abnormal cells, the evaluation of treatments, and drug toxicity testing. Although conventional methods afford cumulative results regarding cell viability based on a great number of cells, they do not permit investigating cell viability at the single-cell level. In response, we rationally designed and synthesized a fluorescent probe, PCV-1, to visualize cell viability under the super-resolution technology of structured illumination microscopy. Given its sensitivity to mitochondrial membrane potential and affinity to DNA, PCV-1's ability to stain mitochondria and nucleoli was observed in live and dead cells, respectively. During cell injury induced by drug treatment, PCV-1's migration from mitochondria to the nucleolus was dynamically visualized at the single-cell level. By extension, harnessing PCV-1's excellent photostability and signal-to-noise ratio and by comparing the fluorescence intensity of the two organelles, mitochondria and nucleoli, we developed a powerful analytical assay named organelle ratiometric probing (ORP) that we applied to quantitatively analyze and efficiently assess the viability of individual cells, thereby enabling deeper insights into the potential mechanisms of cell death. In ORP analysis with PCV-1, we identified 0.3 as the cutoff point for assessing whether adding a given drug will cause apparent cytotoxicity, which greatly expands the probe's applicability. To the best of our knowledge, PCV-1 is the first probe to allow visualizing cell death and cell injury under super-resolution imaging, and our proposed analytical assay using it paves the way for quantifying cell viability at the single-cell level.

A general design of pyridinium-based fluorescent probes for enhancing two-photon microscopy.

Two-photon absorbing fluorescent probes have emerged as powerful imaging tools for subcellular-level monitoring of biological substances and processes, offering advantages such as deep light penetration, minimal photodamage, low autofluorescence, and high spatial resolution. However, existing two-photon absorbing probes still face several limitations, such as small two-photon absorption cross-section, poor water solubility, low membrane permeability, and potentially high toxicity. Herein, we report three small-molecule probes, namely MSP-1arm, Lyso-2arm, and Mito-3arm, composed of a pyridinium center (electron-acceptor) and various methoxystyrene "arms" (electron-donor). These probes exhibit excellent fluorescence quantum yield and decent aqueous solubility. Leveraging the inherent intramolecular charge transfer and excitonic coupling effect, these complexes demonstrate excellent two-photon absorption in the near-infrared region. Notably, Lyso-2arm and Mito-3arm exhibit distinct targeting abilities for lysosomes and mitochondria, respectively. In two-photon microscopy experiments, Mito-3arm outperforms a commercial two-photon absorbing dye in 2D monolayer HeLa cells, delivering enhanced resolution, broader NIR light excitation window, and higher signal-to-noise ratio. Moreover, the two-photon bioimaging of 3D human forebrain organoids confirms the successful deep tissue imaging capabilities of both Lyso-2arm and Mito-3arm. Overall, this work presents a rational design strategy in developing competent two-photon-absorbing probes by varying the number of conjugated "arms" for bioimaging applications.

Quantifying cell viability through organelle ratiometric probing.

Detecting cell viability is crucial in research involving the precancerous discovery of abnormal cells, the evaluation of treatments, and drug toxicity testing. Although conventional methods afford cumulative results regarding cell viability based on a great number of cells, they do not permit investigating cell viability at the single-cell level. In response, we rationally designed and synthesized a fluorescent probe, PCV-1, to visualize cell viability under the super-resolution technology of structured illumination microscopy. Given its sensitivity to mitochondrial membrane potential and affinity to DNA, PCV-1's ability to stain mitochondria and nucleoli was observed in live and dead cells, respectively. During cell injury induced by drug treatment, PCV-1's migration from mitochondria to the nucleolus was dynamically visualized at the single-cell level. By extension, harnessing PCV-1's excellent photostability and signal-to-noise ratio and by comparing the fluorescence intensity of the two organelles, mitochondria and nucleoli, we developed a powerful analytical assay named organelle ratiometric probing (ORP) that we applied to quantitatively analyze and efficiently assess the viability of individual cells, thereby enabling deeper insights into the potential mechanisms of cell death. In ORP analysis with PCV-1, we identified 0.3 as the cutoff point for assessing whether adding a given drug will cause apparent cytotoxicity, which greatly expands the probe's applicability. To the best of our knowledge, PCV-1 is the first probe to allow visualizing cell death and cell injury under super-resolution imaging, and our proposed analytical assay using it paves the way for quantifying cell viability at the single-cell level.

Constant Conversion Rate of Endolysosomes Revealed by a pH-Sensitive Fluorescent Probe.

Endolysosome dynamics plays an important role in autophagosome biogenesis. Hence, imaging the subcellular dynamics of endolysosomes using high-resolution fluorescent imaging techniques would deepen our understanding of autophagy and benefit the development of pharmaceuticals against endosome-related diseases. Taking advantage of the intramolecular charge-transfer mechanism, herein we report a cationic quinolinium-based fluorescent probe (PyQPMe) that exhibits excellent pH-sensitive fluorescence in endolysosomes at different stages of interest. A systematic photophysical and computational study on PyQPMe was carried out to rationalize its highly pH-dependent absorption and emission spectra. The large Stokes shift and strong fluorescence intensity of PyQPMe can effectively reduce the background noise caused by excitation light and microenvironments and provide a high signal-to-noise ratio for high-resolution imaging of endolysosomes. By applying PyQPMe as a small molecular probe in live cells, we were able to reveal a constant conversion rate from early endosomes to late endosomes/lysosomes during autophagy at the submicron level.

Photocatalytic Ketyl Radical Initiated Cketyl -Csp2 /Csp3 Coupling on ZnIn2 S4.

Visible-light-driven C-C bond formation utilizing ketyl radical (Cketyl ) species has attracted increasing attention recently, as it provides a direct route for the synthesis of complex molecules. However, the most-developed homogeneous photocatalytic systems for the generation and utilization of ketyl radicals usually entail noble metal-based (e. g., Ru and Ir) photosensitizers, which suffer from not only high cost but also potential degradation and hence pose challenges in product separation and purification. In contrast, readily accessible, inexpensive, and recyclable semiconductors represent a class of attractive and alternative photocatalysts but remain much less explored for photocatalytic ketyl radical initiated C-C bond formation. This work demonstrates that a wide range of industrially important chemicals, including substituted chromanes and tertiary alcohols, can be produced on ZnIn2 S4 under visible light irradiation through intramolecular cyclization (Cketyl -Csp2 ) and intermolecular cross-coupling (Cketyl -Csp3 ) reactions, respectively, using ketyl radicals. A suite of experimental studies aided by computational investigation were carried out to shed light on the mechanistic insights of these two types of ketyl radical initiated C-C coupling reactions on ZnIn2 S4 .

Derivatized Benzothiazoles as Two-Photon-Absorbing Organic Photosensitizers Active under Near Infrared Light Irradiation.

Homogeneous organic photocatalysis typically requires molecular photosensitizers absorbing in the ultraviolet-visible (UV/vis) region, because UV/vis photons possess the sufficient energy to excite those one-photon-absorbing photosensitizers to the desired excited states. However, UV/vis light irradiation has many potential limitations, especially for large-scale applications, such as low penetration through reaction media, competing absorption by substrates and co-catalysts, and incompatibility with substrates bearing light-sensitive functionalities. In fact, these drawbacks can be effectively avoided if near infrared (NIR) photons can be utilized to drive the target reactions. Herein, we report two benzothiazole-derived compounds as novel two-photon-absorbing (TPA) organic photosensitizers, which can function under NIR light irradiation using inexpensive LED as the light source. We demonstrate that by judicially modulating the donor-π-acceptor-π-donor-conjugated structure containing a bibenzothiazole core and imine bridges, excellent two-photon absorption capability in the NIR region can be achieved, approaching 2000 GM at 850 nm. Together with large quantum yields (∼0.5), these benzothiazole-derived TPA organic photosensitizers exhibit excellent performance in driving various O2-involved organic reactions upon irradiation at 850 nm, showing great penetration depth, superior to that upon blue light irradiation. A suite of photophysical and computational studies were performed to shed light on the underlying electronic states responsible for the observed TPA capability. Overall, this work highlights the promise of developing Ru/Ir-free organic photosensitizers operative in the NIR region by taking advantage of the two-photon absorption mechanism.

Dual hydrogen production from electrocatalytic water reduction coupled with formaldehyde oxidation via a copper-silver electrocatalyst.

The broad employment of water electrolysis for hydrogen (H2) production is restricted by its large voltage requirement and low energy conversion efficiency because of the sluggish oxygen evolution reaction (OER). Herein, we report a strategy to replace OER with a thermodynamically more favorable reaction, the partial oxidation of formaldehyde to formate under alkaline conditions, using a Cu3Ag7 electrocatalyst. Such a strategy not only produces more valuable anodic product than O2 but also releases H2 at the anode with a small voltage input. Density functional theory studies indicate the H2C(OH)O intermediate from formaldehyde hydration can be better stabilized on Cu3Ag7 than on Cu or Ag, leading to a lower C-H cleavage barrier. A two-electrode electrolyzer employing an electrocatalyst of Cu3Ag7(+)||Ni3N/Ni(-) can produce H2 at both anode and cathode simultaneously with an apparent 200% Faradaic efficiency, reaching a current density of 500 mA/cm2 with a cell voltage of only 0.60 V.

Super-resolution analyzing spatial organization of lysosomes with an organic fluorescent probe.

Lysosomes are multifunctional organelles involved in macromolecule degradation, nutrient sensing and autophagy. Live imaging has revealed lysosome subpopulations with dynamics and characteristic cellular localization. An as-yet unanswered question is whether lysosomes are spatially organized to coordinate and integrate their functions. Combined with super-resolution microscopy, we designed a small organic fluorescent probe, TPAE, that targeted lysosomes with a large Stokes shift. When we analyzed the spatial organization of lysosomes against mitochondria in different cell lines with this probe, we discovered different distance distribution patterns between lysosomes and mitochondria during increased autophagy flux. By using SLC25A46 mutation fibroblasts derived from patients containing highly fused mitochondria with low oxidative phosphorylation, we concluded that unhealthy mitochondria redistributed the subcellular localization of lysosomes, which implies a strong connection between mitochondria and lysosomes.

Two-photon-absorbing ruthenium complexes enable near infrared light-driven photocatalysis.

One-photon-absorbing photosensitizers are commonly used in homogeneous photocatalysis which require the absorption of ultraviolet (UV) /visible light to populate the desired excited states with adequate energy and lifetime. Nevertheless, the limited penetration depth and competing absorption by organic substrates of UV/visible light calls upon exploring the utilization of longer-wavelength irradiation, such as near-infrared light (λirr > 700 nm). Despite being found applications in photodynamic therapy and bioimaging, two-photon absorption (TPA), the simultaneous absorption of two photons by one molecule, has been rarely explored in homogeneous photocatalysis. Herein, we report a group of ruthenium polypyridyl complexes possessing TPA capability that can drive a variety of organic transformations upon irradiation with 740 nm light. We demonstrate that these TPA ruthenium complexes can operate in an analogous manner as one-photon-absorbing photosensitizers for both energy-transfer and photoredox reactions, as well as function in concert with a transition metal co-catalyst for metallaphotoredox C-C coupling reactions.

Near-infrared light photocatalysis enabled by a ruthenium complex-integrated metal-organic framework via two-photon absorption.

Photocatalysis under UV/visible light irradiation has emerged as one of the green methodologies for solar energy utilization and organic synthesis. These photocatalytic processes are typically initiated by one-photon-absorbing metal complexes or organic dyes. Nevertheless, the intrinsic restrictions of UV/visible light irradiation, such as shallow penetration in reaction solutions, competing absorption by substrates, and limited coverage of the solar spectrum, call for the development of innovative photocatalysts functioning under longer wavelength irradiation. Herein, we report a ruthenium complex containing a metal-organic framework, MOF-Ru1, which can drive diverse organic reactions under 740 nm light irradiation following the two-photon absorption (TPA) process. Various organic transformations such as energy transfer, reductive, oxidative, and redox neutral reactions were realized using this heterogeneous hybrid photocatalyst. Overall, MOF-Ru1 represents an intriguing TPA photocatalyst active under near-infrared light irradiation, paving a way for the efficient utilization of low-energy light and convenient photocatalyst recycling because of phase separation.

De Novo Design of A Membrane-Anchored Probe for Multidimensional Quantification of Endocytic Dynamics.

As a process of cellular uptake, endocytosis, with gradient acidity in different endocytic vesicles, is vital for the homeostasis of intracellular nutrients and other functions. To study the dynamics of endocytic pathway, a membrane-anchored pH probe, ECGreen, is synthesized to visualize endocytic vesicles under structured illumination microscopy (SIM), a super-resolution technology. Being sensitive to acidity with increasing fluorescence at low pH, ECGreen can differentiate early and late endosomes as well as endolysosomes. Meanwhile, membrane anchoring not only improves the durability of ECGreen, but also provides an excellent anti-photobleaching property for long-time imaging with SIM. Moreover, by taking these advantages of ECGreen, a multidimensional analysis model containing spatial, temporal, and pH information is successfully developed for elucidating the dynamics of endocytic vesicles and their interactions with mitochondria during autophagy, and reveals a fast conversion of endosomes near the plasma membrane.

Defective Ultrathin ZnIn2 S4 for Photoreductive Deuteration of Carbonyls Using D2 O as the Deuterium Source.

Deuterium (D) labeling is of great value in organic synthesis, pharmaceutical industry, and materials science. However, the state-of-the-art deuteration methods generally require noble metal catalysts, expensive deuterium sources, or harsh reaction conditions. Herein, noble metal-free and ultrathin ZnIn2 S4 (ZIS) is reported as an effective photocatalyst for visible light-driven reductive deuteration of carbonyls to produce deuterated alcohols using heavy water (D2 O) as the sole deuterium source. Defective two-dimensional ZIS nanosheets (D-ZIS) are prepared in a surfactant assisted bottom-up route exhibited much enhanced performance than the pristine ZIS counterpart. A systematic study is carried out to elucidate the contributing factors and it is found that the in situ surfactant modification enabled D-ZIS to expose more defect sites for charge carrier separation and active D-species generation, as well as high specific surface area, all of which are beneficial for the desirable deuteration reaction. This work highlights the great potential in developing low-cost semiconductor-based photocatalysts for organic deuteration in D2 O, circumventing expensive deuterium reagents and harsh conditions.

Electrocatalytic synthesis of heterocycles from biomass-derived furfuryl alcohols.

It is very attractive yet underexplored to synthesize heterocyclic moieties pertaining to biologically active molecules from biomass-based starting compounds. Herein, we report an electrocatalytic Achmatowicz reaction for the synthesis of hydropyranones from furfuryl alcohols, which can be readily produced from biomass-derived and industrially available furfural. Taking advantage of photo-induced polymerization of a bipyridyl ligand, we demonstrate the facile preparation of a heterogenized nickel electrocatalyst, which effectively drives the Achmatowicz reaction electrochemically. A suite of characterization techniques and density functional theory computations were performed to aid the understanding of the reaction mechanism. It is rationalized that the unsaturated coordination sphere of nickel sites in our electrocatalyst plays an important role at low applied potential, not only allowing the intimate interaction between the nickel center and furfuryl alcohol but also enabling the transfer of hydroxide from nickel to the bound furfuryl alcohol.

Enhanced Electrocatalytic Hydrogen Oxidation on Ni/NiO/C Derived from a Nickel-Based Metal-Organic Framework.

The sluggish hydrogen oxidation reaction (HOR) under alkaline conditions has hindered the commercialization of hydroxide-exchange membrane hydrogen fuel cells. A low-cost Ni/NiO/C catalyst with abundant Ni/NiO interfacial sites was developed as a competent HOR electrocatalyst in alkaline media. Ni/NiO/C exhibits an HOR activity one order of magnitude higher than that of its parent Ni/C counterpart. Moreover, Ni/NiO/C also shows better stability and CO tolerance than commercial Pt/C in alkaline media, which renders it a very promising HOR electrocatalyst for hydrogen fuel cell applications. Density functional theory (DFT) calculations were also performed to shed light on the enhanced HOR performance of Ni/NiO/C; the DFT results indicate that both hydrogen and hydroxide achieve optimal binding energies at the Ni/NiO interface, resulting from the balanced electronic and oxophilic effects at the Ni/NiO interface.

Interfacing nickel nitride and nickel boosts both electrocatalytic hydrogen evolution and oxidation reactions.

Electrocatalysts of the hydrogen evolution and oxidation reactions (HER and HOR) are of critical importance for the realization of future hydrogen economy. In order to make electrocatalysts economically competitive for large-scale applications, increasing attention has been devoted to developing noble metal-free HER and HOR electrocatalysts especially for alkaline electrolytes due to the promise of emerging hydroxide exchange membrane fuel cells. Herein, we report that interface engineering of Ni3N and Ni results in a unique Ni3N/Ni electrocatalyst which exhibits exceptional HER/HOR activities in aqueous electrolytes. A systematic electrochemical study was carried out to investigate the superior hydrogen electrochemistry catalyzed by Ni3N/Ni, including nearly zero overpotential of catalytic onset, robust long-term durability, unity Faradaic efficiency, and excellent CO tolerance. Density functional theory computations were performed to aid the understanding of the electrochemical results and suggested that the real active sites are located at the interface between Ni3N and Ni.

Electrocatalytic and photocatalytic hydrogen evolution integrated with organic oxidation.

Renewable energy-driven hydrogen production from electrocatalytic and photocatalytic water splitting has been widely recognized as a promising approach to utilize green energy resources and hence reduces our dependence on legacy fossil fuels as well as alleviates net carbon dioxide emissions. The realization of large-scale water splitting, however, is mainly impeded by its slow kinetics, particularly because of its sluggish anodic half reaction, the oxygen evolution reaction (OER), whose product O2 is ironically not of high value. In fact, the co-production of H2 and O2 in conventional water electrolysis may result in the formation of explosive H2/O2 gas mixtures due to gas crossover and reactive oxygen species (ROS); both pose safety concerns and shorten the lifetimes of water splitting cells. With these considerations in mind, replacing the OER with thermodynamically more favorable organic oxidation reactions is much more preferred, which will not only substantially reduce the voltage input for H2 evolution from water and avoid the generation of H2/O2 gas mixtures and ROS, but also possibly lead to the co-production of value-added organic products on the anode. Indeed, such an innovative strategy for H2 production integrated with valuable organic oxidation has attracted increasing attention in both electrocatalysis and photocatalysis. This feature article showcases the most recent examples along this endeavor. As exemplified in the main text, the oxidative transformation of a variety of organic substrates, including alcohols, ammonia, urea, hydrazine, and biomass-derived intermediate chemicals, can be integrated with energy-efficient H2 evolution. We specifically highlight the importance of oxidative biomass valorization coupled with H2 production, as biomass is the only green carbon source whose scale is comparable to fossil fuels. Finally, the remaining challenges and future opportunities are also discussed.

Visible-Light-Driven Valorization of Biomass Intermediates Integrated with H2 Production Catalyzed by Ultrathin Ni/CdS Nanosheets.

Photocatalytic upgrading of crucial biomass-derived intermediate chemicals (i.e., furfural alcohol, 5-hydroxymethylfurfural (HMF)) to value-added products (aldehydes and acids) was carried out on ultrathin CdS nanosheets (thickness ∼1 nm) decorated with nickel (Ni/CdS). More importantly, simultaneous H2 production was realized upon visible light irradiation under ambient conditions utilizing these biomass intermediates as proton sources. The remarkable difference in the rates of transformation of furfural alcohol and HMF to their corresponding aldehydes in neutral water was observed and investigated. Aided by theoretical computation, it was rationalized that the slightly stronger binding affinity of the aldehyde group in HMF to Ni/CdS resulted in the lower transformation of HMF to 2,5-diformylfuran compared to that of furfural alcohol to furfural. Nevertheless, photocatalytic oxidation of furfural alcohol and HMF under alkaline conditions led to complete transformation to the respective carboxylates with concomitant production of H2.

NiSe@NiOOH Core-Shell Hyacinth-like Nanostructures on Nickel Foam Synthesized by in Situ Electrochemical Oxidation as an Efficient Electrocatalyst for the Oxygen Evolution Reaction.

NiSe@NiOOH core-shell hyacinth-like nanostructures supported on nickel foam (NF) have been successfully synthesized by a facile solvothermal selenization and subsequent in situ electrochemical oxidation (ISEO). First, the unique NiSe/NF nanopillar arrays were prepared in N,N-dimethylformamide (DMF) as a precursor template that can provide a large surface area, excellent conductivity, and robust support. Next, amorphous NiOOH covering the surface of NiSe nanopillars was fabricated by ISEO, as confirmed by XPS andEDX spectroscopy. SEM images revealed the hyacinth-like morphology of NiSe@NiOOH/NF with NiOOH as the shell and NiSe as the core. The electrochemical performance of NiSe@NiOOH/NF for the oxygen evolution reaction (OER) was investigated. NiSe@NiOOH/NF demonstrates an obviously enhanced OER activity with much lower overpotential of 332 mV at 50 mA cm(-2) compared to other Ni-based electrocatalysts. The low charge-transfer resistance (Rct), large electrochemical double-layer capacitance (Cdl) of electrochemically active surface areas (ECSAs), and excellent long-term stability of NiSe@NiOOH/NF confirm the enhancement of its electrochemical performance for the OER, which can be ascribed to the large amount of active sites derived from the amorphous NiOOH shell and the good conductivity and stability derived from the NiSe core. In addition, the synergistic effect between the NiSe core and NiOOH shell could serve for a highly efficient OER electrocatalyst.